The Richat Structure,also known as the “Eye of Africa”, is a prominent circular feature in the Sahara’s Adrar Plateau, in west–central Mauritania. The structure is a deeply eroded dome with a total diameter of almost 50 km, while the center of concentric rings is 30 km width. These concentric rings are actually alternating layers of sedimentary, metamorphic, and igneous rocks that were pushed upward in a symmetrical anticline, geologic dome, from below due to a small incursion of magma.
By NASA – https://www.flickr.com/photos/nasa2explore/16824767220/, Public Domain, Link
By NASA – http://eol.jsc.nasa.gov/SearchPhotos/photo.pl?mission=ISS042&roll=E&frame=007126, Public Domain, Link
Public Domain, Link